As a rule, valve prostheses are introduced into the body as an integrated part of vessel supporting prostheses. Such supporting prostheses are as a rule tubular lattice structures which are also referred to as “stents”. Supporting prostheses with integrated valve replacement are known in the prior art. Such valves are obtained from cow, from pig as well as from horse. Supporting prostheses with tissue engineered (“TE”) valves are also known (Stock et al. (2006). J. Thorac. Cardiovasc. Surg. 131, 1323-30). As compared to a xenograft, tissue engineering in general offers the advantage that cells of any desired origin (e.g. homologous or autologous human cells) can be integrated into the structure of an existing decellularized, non-human valve (see EP 1499366).
However, implanting such supporting prostheses with TE valves has proven to be extremely difficult in practice, since TE valves as a rule are very sensitive. For instance, when they are introduced into the body inside a supporting prosthesis made of for example metal, such valves can be ripped or crushed by this supporting prosthesis and/or become caught within the supporting prosthesis. This leads to undesirable damage of the valve disposed in the stent. In a TE valve damaged in this way, degeneration and/or malfunction of the valve can result.
In the prior art, this problem has been solved by lining the inside of a valve-containing stent with xenograft tissue. For instance, a mucosa layer from the pig small intestine was sutured to the inside of a metal stent. Subsequently, a pulmonary valve was connected with this mucosal layer. The mucosal layer served as a sort of shield against the metal structure of the stent which could potentially damage the valve (Stock et al. (2006). J. Thorac. Cardiovasc. Surg. 131, 1323-30.) It has been determined that the heart valve in such a stent lined on its inside with tissue was less severely damaged than valves in stents which comprised no tissue layer of any sort, or a tissue layer only on the outside.
Nevertheless, such prostheses lined on their inside with tissue layers are associated with significant disadvantages. First, the preparation for implantation is complicated by the necessity of attaching an additional layer on the inside of the stent. Second, the use of tissue layers of non-human origin implies significant risks with regard to an infection and/or transplant rejection in the human patient. On the other hand, it would be difficult to isolate sufficient quantities of autologous mucosal layer for lining the stent to be introduced from every patient needing a valve prosthesis.
Independent of these disadvantages in known stents containing a replacement valve, significant difficulties exist in the special context of the aortic valve prostheses. These difficulties result partially from the general sensitivity of valve prostheses as explained above, but also from the anatomical particularities in he aorta region in particular. Due the high blood pressure in the aorta region, the aorta tissue is subjected to exceptional physical strains. In order to withstand these strains while still fulfilling its supporting functions, a stent intended for the aorta region must therefore be robust, wherein a rigidity in the stent structure may mean a great danger of damage for the valve located therein. Further, the introduction of a very robust stent in the region of the aorta brings with it the danger that other vessels important for life, such as for example the coronary arteries ostium dextra and ostium sinistra descending on both sides of the aorta are disrupted in their function.
It is thus an aim of the present invention to provide an improved stent with valve replacement which enables the implantation of a sensitive TE valve in regions of great strain such as in the aorta, where in the disadvantages mentioned above are avoided.